MFACs were widely used; but are now being phased out because of concerns over contamination of the environment with lead compounds, and incompatibility of MFAC-treated fuels with catalytic devices used to minimize motor exhaust emissions of hydrocarbons, carbon monoxide, and oxides of nitrogen. Manufacturing and distribution equipment worldwide is frequently contaminated with components of MFACs. Contaminated sludges typically also exist in this equipment. In many cases soils at MFAC and petroleum refinery manufacturing and storage sites, as well as commercial gasoline storage areas, have been contaminated with these same MFAC components. The primary MFAC components of concern comprise at least one tetraalkyllead ingredient, (e.g., tetraethyllead, TEL, and/or tetramethyllead, TML, and solvents and scavengers such as 1,2-dichloroethane (ethylene dichloride, EDC), 1,2- dibromoethane (ethylene dibromide, EDB), among others. These components of MFAC are toxic and, thus, treatment of contaminated equipment, sludges, and soils is usually required prior to their disposal or reclamation.
While several alkylleads have been used, by far the most prevalent one is TEL, tetraethyllead. TEL is not stored or sold as a pure chemical due to its thermal and storage instability. The EDC and/or EDB serve as stabilizers in storage and as lead scavengers when the TEL breaks down in the internal combustion engine. The MFAC can be used to raise the octane value of motor gasoline to prevent knocking. MFAC is manufactured in two grades, TEL Motor Antiknock and TEL Aviation Antiknock. Commercially available TEL Motor Antiknock is a mixture of TEL (61.5% by wt.) in ethylene dichloride (18.8%), ethylene dibromide (17.9%), and kerosene (1.8%). Commercially available TEL Aviation Antiknock is a mixture of TEL (61.5%), EDB (35.7%), and kerosene (2.8%), and can be used in aviation gasoline for piston engine aircraft.
MFAC can be transported to refineries by rail tank cars, tank trucks, and by ship worldwide. Spills may occur at the various terminals and storage facilities thereby creating MFAC-contaminated soil.
MFAC can be unloaded into weigh tanks at the refinery. MFAC can be metered from these tanks into the gasoline to make "leaded" gasoline. TEL slowly decomposes to lead oxides, lead bromides, and lead hydroxybromides in these weigh tanks. Corrosion of the interior tank surfaces normally forms an iron oxide deposit or scale, e.g., lead and iron salts, within the tank. This scale comprises a dense, heterogeneous material with TEL, EDC, and EDB adsorbed onto the deposit or scale.
TEL contaminated sludge (and soil contaminated with TEL) arises at the alkyllead manufacturing facility. The wash water waste stream from the TEL manufacturing process contains fine particulate lead. This water stream is typically fed to a settling basin to allow the solids to settle prior to the water being discharged. Due to the insolubility of TEL in water (0.8 ppm), it is found adhered to this sludge deposited in the settling ponds. Air oxidation of the fine lead affords lead oxide, which under the alkaline conditions of the waste stream readily combines with carbon dioxide to form basic lead carbonate [2PbCO3.Pb(OH)2], the predominant inorganic constituent of the sludge. The basic lead carbonate typically is contaminated with significant quantities of adsorbed TEL.
Various treatment methods are known or have been proposed for treating contaminated environments. The use of surfactants, including nonionic surfactants, in aqueous solution to emulsify oily contaminants is well known For instance, Newcombe and Doane in U.S. Pat. No. 2,748,080 and Doscher and Reisberg in U.S. Pat. No. 2,882,973 disclose such techniques for recovering oil from tar sands.
It is also known that hydrophobic contaminants can be removed from surfaces with aqueous surfactants to effect decontamination using co-solvents or modifiers such as kerosene. One example is disclosed by U.S. Pat. No. 4,783,263 wherein procedures for using flotation cells and modifiers in order to remove a range of contaminants, including tetraethyllead.
Other examples of known procedures are disclosed in U.S. Pat. Nos. 5,055,196 and 5,122,194 that relate to processes for removing polychlorinated biphenyls (PCBs) by treating soils and sludges with a solvent, such as hexane or kerosene, and an aqueous surfactant solution.
In a different area of technology, Ikura et al. in U.S. Pat. No. 5,120,428 disclose methods for selecting surfactants for processes to deash (remove mineral or ash constituents) heavy hydrocarbon residues, such as those resulting from coal liquefaction. Ikura et al. select surfactants with hydrophile-lipophile balance values (HLB) between 1 and 6 for creating a water-in-oil emulsion and a surfactant with HLB values higher than 15 to render the dispersed ash more hydrophilic, concentrating the undesired ash from the oil phase to the water phase for disposal.
M. J. Rosen, Surfactants and Interfacial Phenomena, 2nd Ed., John Wiley & Sons, (1989) discloses techniques to select surfactants based on HLB values.
Another conventional method relates to soil flushing, and has been reviewed by the U.S. Environmental Protection Agency (EPA). In the Agency's Handbook on In Situ Treatment of Hazardous Waste-Contaminated Soils [EPA/540/2-90/001, January 1990], flushing with aqueous surfactant solutions, including nonionic surfactants, is discussed in Section 3.
The disclosure of each of the above-identified patents and references is hereby incorporated by reference.